The present invention relates to: a method for operating an internal combustion engine, e.g., of a motor vehicle, where the fuel is supplied under pressure via an injection valve and the injected fuel quantity is influenced by the injection time.
Such a method is typically used for internal combustion engines that include a throttle,valve that is not mechanically connected to the gas pedal, e.g., of a motor vehicle. It functions according to the principle of direct gasoline injection (DGI), where the fuel;is injected with high pressure directly into a combustion chamber of the internal combustion engine. The injection is performed in this context via an injection valve that is controlled by a control and/or regulating device such that it is open for a certain period of time. Therefore, in the conventional method, the fuel quantity injected into the combustion chamber is determined or influenced by the injection time.
The basis of the direct gasoline injection is a fuel system that supplies the fuel under high pressure to the injection valves. If the actual fuel pressure deviates from a setpoint pressure range due to a fault in the fuel system, this may lead to the injected fuel quantity not corresponding to the required fuel quantity despite a correct opening period of the injection valve.
For this reason, the injection period is corrected in the case of the conventional method as a function of the fuel pressure. The corrected injection period may, however, be longer than the maximum timing window available for injection. In this case, the injection is discontinued. This results in an air-fuel mixture in the combustion chamber that may not correspond to the required air-fuel mixture. Such an air-fuel mixture may be lean, for example, which may result in a break in the torque or even misfires of the internal combustion engine. Moreover, the emission characteristics of an internal combustion engine that is operated in this manner suffer.
The indicated problems occur above all in the case of high rotational speeds and a correspondingly high required fuel quantity to be injected. In the case of the conventional method, the maximum possible rotational speed of the internal combustion engine is restricted when the fuel pressure deviates from a setpoint pressure range. However, this results in a significant loss of comfort in operation of the internal combustion engine, e.g., in connection with the operation of the internal combustion engine in a motor vehicle, since a large operating range of the internal combustion engine is no longer available. Moreover, it may occur that a temperature drop needed to protect, for example, an exhaust gas turbine or a catalytic converter by appropriately enriching the mixture is no longer possible.
Therefore, it is an object of the present invention to further develop a method such that the internal combustion engine may be able to be operated at a relatively high comfort level even in the event of a fault in the fuel system, and a lifetime of the internal combustion engine and its components that is as long as possible is ensured.
This object may be achieved by determining a maximum allowable torque of the internal combustion engine that is dependent on the actual fuel pressure.
According to the present invention, in the event of a fault in the fuel system of the internal combustion engine, the engine may be operated at high rotational speeds without having to fear damage to the internal combustion engine. The cause of possible damage to the internal combustion engine in the event of a fault in the fuel system is not the high rotational speeds, but the incorrect air-fuel mixture in the combustion chamber due to the incorrect injected fuel quantity. The effects may be perceptible at a high actual rotational speed of the internal combustion engine.
By restricting the maximum torque of the internal combustion engine, it may be possible to us,e the entire speed range of the internal combustion engine. Thus, in accordance with the present invention, the internal combustion engine may be able to be operated at very high rotational speeds as long as only a small fuel quantity must be injected in this speed range. This is the case when a relatively low torque must be provided in the internal combustion engine.
In the case of a motor vehicle, such situations may be present, e.g., during a downhill run, e.g., when operating the motor vehicle with a trailer.
In a first further refinement, the maximum allowable torque may be acquired from a restriction of a maximum air charge of a combustion chamber. The air charge of the combustion chamber may be a value that is easy to set for conventional internal combustion engines. In the case of internal combustion engines where the throttle valve is not mechanically connected to a gas pedal (so-called EGAS), the air charge may be able to be simply adjusted by appropriately controlling the throttle valve. In the case of internal combustion engines having precompression (turbo charger), a recirculation valve is typically able to be actuated via which the boost pressure, i.e., ultimately the air charge of the combustion chamber, is able to be adjusted.
An object of the method is to adjust a certain fuel-air mixture in the combustion chamber even in the event of a fault in the fuel system. This may be possible, for example, in that the maximum air charge from which the maximum allowable torque is acquired is determined on the basis of the maximum injectable fuel quantity.
This may be determined from the instantaneous rotational speed, the maximum possible injection time, and the available fuel pressure. Such a determination of the maximum injectable fuel quantity may lend itself when the fault in the fuel system is due to the pressure being too low. Such a fault may occur in the case of a defective fuel pump, for example.
A pressure of the fuel system that is below a setpoint pressure range may cause the maximum injectable fuel quantity to decrease since during the opening period of the injection valve, i.e., the injection time, only a minimal fuel quantity emerges from the injection valve. The maximum injection time possible at a certain rotational speed then results from the maximum possible rotational speed of the internal combustion engine and the maximum valve-specific and/or internal combustion engine-specific injection time possible at this rotational speed (this is then generally dependent on the earliest possible injection start and the ignition firing point).
However, a fault in the fuel system may also result in a fuel pressure that is too high. This may occur, for example, when a pressure control valve in the fuel system is defective. To be able to permit the injection valve to reliably open in the case of a fuel pressure that is too high, the holding current of the injection valve must be increased. However, an increased holding current may result in a significant increase in power loss in a control unit; of the injection valves, which then results in this control unit being thermally stressed. In a further refinement of the method of the present invention, this is countered in that the maximum injectable fuel quantity may be determined from the instantaneous rotational speed, a holding current of the injection valve, and the fuel pressure.
Since restricting the maximum torque of the internal combustion engine may significantly affect the operating characteristics of the internal combustion engine, in a further refinement of the method of the present invention, a detected deviation results in an error message. In the case of a motor vehicle, such an error message informs the driver that the normal torque of the internal combustion engine is not available. As such, the drive is able to adapt his/her driving technique to the changed characteristic of the internal combustion engine.
The present invention also relates to a computer program that is suited for implementing the above method when it is performed on a computer. In this context, the computer program may be stored on a memory, e.g., on a flash memory.
Finally, the present invention also relates to a control and/or regulating device for operating an internal combustion engine, e.g., of a motor vehicle, where the fuel is supplied under pressure via at least one injection valve, and the injected fuel quantity is influenced by the injection time.
In order to be able to provide the user with the maximum comfort during operation of the internal combustion engine in the event of a deviation of the ;fuel pressure from a setpoint pressure range, in accordance with the present invention, the control and/or regulating device determine a maximum allowable torque of the internal combustion engine that is dependent on the actual fuel pressure. With regard to the control and/or regulating device of the present invention, reference is made to the explanations above.